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Like all deciduous fruit trees, pear trees produce growth inhibitor hormones in the fall that initiate a period of dormancy not broken until the trees experience enough chill hours. The required number of chill hours, when the temperature is between 32 and 45 degrees F, varies with the cultivar. For the typical European pear (Pyrus communis), 600 to 900 chill hours ensure an ample crop, while the round Asian pears (P. serotina) need less, some fewer than 400 hours.

Dormancy and Chill Hours

As part of its annual cycle, a pear tree's growth stops as days shorten and temperatures decrease. Following this, the tree drops its leaves, and its internal processes enter dormancy, a state of rest. Dormancy prevents the tree from beginning to grow again when atypical warm spells occur in winter. Otherwise, the plant could be damaged if normal freezing temperatures return. Dormancy is only broken when sufficient periods of cold temperature cause the growth inhibitors within the tree to cease functioning. "Bartlett," the most widely grown pear, needs 800 chill hours to reach this point. Other European pears, such as "Comice" and "Seckel," require 200 to 600 hours and 300 to 800 hours, respectively. The Asian pear "Hosui" can get by with 450 chill hours. While pear trees are dormant, the time is right for a number of garden tasks.

Planting Trees

December to March is the season to plant bare-root pear trees. Because pears are among the longest-lived fruit trees, carefully choose the cultivar and rootstock. Dwarf fruit trees tend to produce inferior fruit, so standard or semi-dwarf specimens may be wiser choices. Though standard trees can grow to 40 feet, it is possible to dwarf them by strict pruning and training. Pear trees thrive in sunny spots in well-drained loam but tolerate poorer soils better than most fruit trees.

Pruning Time

Winter, when the trees are dormant, is the best time to prune them. Remove 15 to 20 percent of last year's growth, so light can enter the tree's center. Pear trees produce fruit on spurs that are two to three years old. Preserve these fruiting spurs when pruning. Beginning with a tree's first blooming season, follow the same pruning pattern. First, remove diseased or broken limbs. If two branches are growing from the same spot, cut away the weaker one. Do the same if two branches cross or rub against each other. Thin out whip-like shoots coming from the center of the tree. Allowing sunlight and air to flow easily to the tree's center is essential to its health and productivity.

Insect and Disease Protection

If aphids, scale insects or mites cause recurring problems for your pear trees, apply a dormant oil spray in the winter. To help control powdery mildew, rake up and remove fallen leaves in the orchard. Pears are particularly susceptible to fireblight, a bacterial disease that causes twig ends and leaves to develop a burnt look and suddenly die. If fireblight is suspected, remove the affected parts immediately and burn them or dispose of them in sealed bags. Make your pruning cuts in healthy wood, back at least 12 inches from the diseased portion. After each cut, pruning shears need to be disinfected by dipping in isopropyl alcohol.

About the Author

Mary Simpson began her writing career in 1968 on a Dallas oil magazine. Besides reporting and editing for several small Texas newspapers, Simpson has written for "Petroleum Engineer Magazine," "Denton Today Magazine" and put out an employee newsletter for a FEMA facility. She holds a B.A. in journalism and an M.A.in English, both from the University of North Texas.